1. Field of the Invention
The present invention relates to USB chargers and more particularly, to a USB charging circuit, which uses a synchronization/charge mode switching circuit to detect the connection of an external computer, and a USB charging control circuit to control output of power and data to each connected portable electronic device. The USB charging circuit employs a complete hardware logical judgment technique for output control, saving the cost, enhancing charging speed and achieving synchronous multi-port data transmission operation.
2. Description of the Related Art
With fast development of semiconductor manufacturing process and multimedia information technologies, notebook computers, tablet computers, smart phones, PDAs and many other electronic devices have been created having light, thin, short, small and powerful characteristics. Due to the advantages of small size, light weight, high mobility, high application flexibility and practicability and advanced hardware and software configurations, these mobile electronic devices are intensively used to substitute for home computers. Further, the introduction of touch control techniques eliminates the use of complicated operating interface and enables a direct interactive mode to educational systems, such as museum navigation systems, electronic book systems, school education systems and so on.
Further, today information technology is well developed, the learning environment is being constantly changed and improved. In order to satisfy people's desire for knowledge and to improve interactive flexibility in education and learning, data software expansibility of portable electronic devices must be considered.
Further, companies, schools and government or private organizations may purchase a, large amount of portable electronic devices to meet different data classification and software requirements. However, charging a large amount of portable electronic devices that consume different voltages requires a large amount of electrical outlets and voltage converters, complicating the arrangement of power cables and charging systems and the charging operation.
Further, USB interface is the most popularly used connection interface for data transmission and battery charging application. A standard USB port simply provides 500 mA low-current output. Many portable electronic devices can accept 2.1 A charging current. If 500 mA is used to charge a portable electronic device, the charging speed is relatively slow. Further, using a USB port for data update and charging simply allows one-to-one transmission. It will take a lot of time to charge or update a large amount of portable electronic devices.